Selective alternating-direct-current system.



J. F. TRITLE. SELECTIVE ALTERNATING DIRECT CURRENT SYSTEM. APPLICATION FILED JULY 27,1908.

' 1 28,405. Patented June 4, 1912.

I Wifnesses I lnventon 9 $041 John fiTriifle,

UNITED STATES PATENT QI I IQEQ JOHN F. TRITLE, OF S'GHENECTADY, YORK, ASSIG-NOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SELECTIVE ALTEBNATING-DIBEGT-CURRENT SYSTEM.

To all whom it may concern:

Be it known that I, JOHN F. Tnrrnn, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Selective Alternating-Direct-Current Systems, of which the following is a specification.

In electrically driven cars intended for operation either on alternating or direct current, usually high potential alternating current and low potential direct current, the change from one to the other being ordinarily made while the car is moving, it is customary to provide a system of selective switches arranged to automatically connect the current collecting device to the proper circuits of the car for either alternating or direct current operation. Such a system of selective switches is shown in the patent to Frank andPevear, No. 854,730, dated May 28, 1907, control of electric cars. The arrangement there shown consists of a small step-down transformer having its primary connected to the power circuit, the actuating coil of the A. C. switch being connected across the secondary of said transformer, and the actuating coil of the D. C. switch being in series with the primary of said transformer. With this arrangement the A. C. switch is operated only when the current collecting device is receiving alternating current, and the D. C. switch is supposed to operate only when the current collecting device connects with a source of direct current. It has been found in actual practice that a system such as that mentioned above may be open to the objection that when the car enters an alternating current section the first rush of current through the primary of the transformer, before the counter E. M. F. of the transformer has had time to build up, may operate the D. C. switch. Such an occurrence is, of course, highly objectionable, and in order to prevent it a short-circuited band has been placed on the core of the operating magnet of the D. C. switch, as set forth on the patent above referred to, this band serving as the secondary of a transformer of which the primary is the actuat ing coil of the D. C. switch. With this arrangement the flux in the magnet of the D. C. switch, resulting from a flow of alternating current, is reduced below the value necessary to close the switch and its opera- Specification of Letters Patent.

Application filed July 27, 1968.

Patented June 4, 1912.

Serial No. 445,445.

tion on alternating current is prevented. Instead of a short-circuited band used as above described, I have found that the same result may be attained by short-circuiting a portion of the actuating coil of the D. C. switch through contacts closed by this switch when it is open, as set forth in my oo-pending application, Serial No. 411,453, filed January 18, 1908.

While the arrangements above described are satisfactory under most conditions of operation, in an exceptional case it may occur that the D. C. switch will close on alternating current, and an object of my invention is to provide means whereby this objectionable operation is more effectively and certainly prevented.

To this end, my invention consists in employing, in a system of the general nature of the one above described, means connected in shunt to the actuating coil of the D. C. switch which will permit the passage of current at the high potential of the alternating current section but will not allow current to pass through it at the lower potential of the direct current section. A lightning arrester possesses the necessary qualifications for this purpose and I have herein shown my invention carried out with this kind of apparatus. When a lightning arrester is employed in this way, the D. C. switch may or may not be provided with a short-circuiting band or coil as above mentioned. In order, however, to provide for greater safety the short-circuiting band is preferably employed. While it is obvious that other forms of lightning arrester may be employed, I have found that the socalled aluminum cell type is especially well adapted for this purpose and I have in this application illustrated my invention as carried out with this type of protective apparatus. The lightning arrester of the type referred to is disclosed in a co-pending application in the name of Elmer E. F. Creighton, Serial No. 325,195, filed July 9, 1906, assigned to the same assignee as this application, and comprises a series of aluminum dishes or cells nested together and filled with a suitable electrolyte.

My invention will be best understood from the following description taken in connection with the accompanying drawing, in which I have shown diagrammatically one form in which it may be embodied.

I deem it unnecessary to illustrate any system of motor control as it is obvious that my invention is not limited in its application to any particular control system. Furthermore, while I have shown my system as arranged for use on electrically driven cars, it is obvious that it may equally well be used in other connections.

Referring to the drawing, L represents the trolley wire or other supply conductor with which the trolley T or other current collecting device carried by the car engages. It is to be assumed that the supply conductor is at some places on the line supplied with alternating, and at other places with, direct current, the potential of the alternating current section being usually high, for example, 6600 volts, and the potential of the direct current section being relatively low, for example, 600 volts.

The usual kicking coil and lightning arrester are diagrannnatically indicated at A.

The main switch which is intended to close only on alternating current operation is indicated at S, and the main switch which closes only on direct current operation is shown at S These switches S and S may be of any suitable design. A small stepdown transformer represented at E is shown with its primary connected between trolley and ground. The actuating coil 1 of the A. C. switch S is connected across the secondary of the transformer E, and the actuating coil 2 of the D. C. switch S is arranged in series with the primary of the transformer E. This coil 2 is connected permanently to ground through a non-inductive resistance 3 and is also connected to ground through auxiliary switches 4 and 5 opened by the D. C. switch S when the latter is closed. One of the auxiliary switches 5 is provided with a magnetic blow-out and is arranged to open after and to close before the auxiliary switch 4:, thereby confining the arcing to the switch 5 and keeping the contacts of the switch 4- in condition to make good electrical connection with one another. The magnetic core of the switch S may be provided with a short circuit band 6, if desired, as mentioned above.

An auxiliary switch 7 closed by the A. C. switch S in closing connects the primary of the transformer E directly to ground, thereby shunting the coil 2 of the D. C. switch S after the switch S has closed.

A lightning arrester, diagrammatically indicated at S and preferably of the aluminum cell type referred to above, is connected in shunt to the actuating coil 2 of the D. C. switch S The actuating coil 2 of the D. C. switch is so designed that the voltage at which this switch will close on alternating current is considerably higher than the critical or break down voltage of the lightning arrester, while the voltage at which the switch will close on direct current is considerably below the break-down Voltage of the lightning arrester. Owing to the inductance of its actuating coil, an electrically operated switch always requires a higher potential for operation on alternating current than for operation on direct current, and this difference in the two operating potentials may be made greater or less, in a well known manner, by increasing or decreasing the inductance of the actuating coil, for instance, by increasing or decreasing the number of turns in the coil. With this arrangement the actuating coil 2 is relieved from any rush of alternating current which might be sufficient to cause the switch S to 'close, and yet at the same time the current passing through the lightning arrester when the car is operating on direct current is very small.

The operation of my selective system is as follows: If the current collecting device engages with a supply conductor furnishing alternating current at high potential, the first heavy rush of current will flow through the primary of the transformer E, through the lightning arrester 8 and in parallel paths through the auxiliary switches 4: and 5 and the resistance 3 to ground, since at this high potential the lightning arrester breaks down. Under this condition the amount of current flowing through the actuating coil 2 will. be small and there will be no danger of the D. 0. switch closing. The actuating coil 1 of the A. 0. switch will, however, be energized from the secondary of the transformer E and the switch S will close. The switch S in closing closes the auxiliary switch 7 and connects the primary of the transformer E directly to ground through a path in shunt to the circuit through the lightning arrester 8 and the coil 2. If, on the other hand, the current collecting device T engages with a supply conductor furnishing direct current, current will flow through the primary of the transformer E, the actuating coil 2 of the switch S and through the auxiliary switches 4 and 5 to ground. The D. 0. switch will, therefore, close and by opening the auxiliary switches 4: and 5 will throw the resistance 3 into circuit with the coil 2, thereby reducing the current through this coil and preventing heating of the latter.

On D. C. operation no appreciable current will pass through the lightning arrester 8 since, as is stated above, the break-down value of the lightning arrester is above the voltage supplied on D. C. operation.

Any condenser action which the lightning arrester 8 may have is doubtless of benefit in the operation of the system, but I do not consider that it is essential to the successful operation of my invention that the lightning arrester shall act as a condenser.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. A selective high potential alternating and low potential direct current system for electric cars comprising a transformer having its primary connected to the power circuit, an A. C. switch, a D. C. switch, an actuating coil for said A. C. switch connected across the secondary of said transformer, an actuating coil for said D. C. switch connected in series with the primary of said transformer, and means connected in shunt to the actuating coil of said D. C. switch acting as a conductor on high potential A. C. operation and as a non-conductor on low potential D. C. operation.

2. A selective alternating-direct current system for electric cars comprising a transformer having its primary connected to the power circuit, an A. C. switch, a D. C. switch, an actuating coil for said A. C. switch connected across the secondary of said transformer, an actuating coil for said D. G. switch connected in series with the primary of said transformer, and means connected in circuit with one of said actu ating coils for controlling the operation thereof, said, means heing conductive on alternating current when a voltage is applied thereto which is less than that required to operate the D. 0. switch and nonconductive on direct current at the voltage at which said D. 0. switch will close.

3. A selective alternating-direct current system for electric cars comprising a transformer having its primary connected to the power circuit, an A. 0. switch, a D. C. switch, an actuating coil for said A. 0. switch connected across the secondary of said transformer, an actuating coil for said D. G. switch connected in series with the primary of said transformer, and a lightning arrester connected in shunt to the actuating coil of said D. G. switch.

4. A selective alternating-direct current system for electric cars comprising a transformer having its primary connected to the power circuit, an A. C. switch, a D. 0. switch, an actuating coil for said A. C. switch connected across the secondary of said transformer, an actuating coil for said D. C. switch connected in series with the primary of said transformer, and a lightning arrester of the aluminum cell type connected in shunt to the actuating coil of said D. 0. switch.

In witness whereof, I have hereunto set my hand this 25th day of July, 1908.

JOHN F. TRITLE.

Witnesses:

HELEN Onrono, BENJAMIN B. HULL.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

